1. Field of the Invention
This invention relates to an improvement on a microphone-unit supporting structure in a microphone-element-equipped electronic device such as a portable radio communication device. This invention particularly relates to a microphone-unit supporting structure which can secure a microphone unit in an electronic device while providing a good waterproof performance and an excellent reproducibility during assembly.
2. Description of the Related Art
For a microphone-element-equipped electronic device such as a radio communication device, a telephone set, a personal computer, a speech recognition device, or an interphone device, it is desirable to surely locate and secure a microphone element in the electronic device while proving a good waterproof performance with respect to the microphone element.
In the case where the microphone element is directly fixed to a main printed circuit board of the electronic device, output terminals provided on the back of the microphone element are soldered to a wiring pattern on the main printed circuit board so that the microphone element is electrically connected to the wiring pattern while being mechanically fixed to the main printed circuit board.
In this case, the position of the microphone element relative to the main printed circuit board is uniquely decided, and hence there may occur a low degree of freedom of a structural layout in the electronic device. When the microphone element is located at a deep position within a casing of the electronic device, the sound propagation path between the microphone element and an outer plane of the casing is relatively long so that the quality of sound picked up by the microphone element tends to be lowered.
Japanese patent application publication number 11-68259 discloses that a portion of a main printed circuit board forms a sub printed circuit board provided with a microphone. Leads connected between the main board and the sub board establish electrical connection of the microphone to the main board. The sub board can easily be separated from the main board. After separated from the main board, the microphone on the sub board is fitted into a recess in a casing accommodating the main board.
In Japanese application 11-68259, it seems that the microphone can be fitted into the recess while taking any one of different postures angularly spaced at 90-degree intervals. Accordingly, there is a chance that during assembly, a worker may make a mistake about the angular orientation of the microphone relative to the recess.
To allow a microphone element to pick up sound from the outside of a casing, the microphone element is positioned within the casing at a place which communicates with the outside via a hole or holes. In the case where a microphone element separates the interior of a casing into a space accommodating a main printed circuit board and a space communicating with the outside of the casing, it is conceivable to provide an elastic packing member around the microphone element to make a waterproof structure. Variations in microphone element size, microphone element position relative to a related printed circuit board, microphone element position relative to a related casing, and microphone element position relative to the packing member are absorbed only by the elasticity of the packing member. When greatly deformed from its original shape to absorb such variations, the packing member receives an excessive stress. Such an excessive stress accelerates the deterioration of the waterproofness provided by the packing member.